von Willebrand factor competes with fibrin for occupancy of GPIIb:IIIa on thrombin-stimulated platelets.
We have investigated two major questions related to the molecular basis of interactions between the three-dimensional fibrin network and thrombin-stimulated human platelets. First, what are the roles played by glycoproteins (GP) Ib and IIb:IIIa in linking the fibrin clot tightly to the platelet surface? Second, does von Willebrand factor (vWF) modulate the extent of platelet-fibrin interactions? Quantitative fluorescence microscopy (microfluorimetry) has been used to determine the quantity of fluorescein-labeled fibrin bound to the surface of thrombin-stimulated, gel-filtered platelets (the supernatants of which contained small quantities of vWF) in the presence/absence of receptor-specific and vWF-specific monoclonal antibodies (MoAbs), as well as exogenous vWF. A MoAb specific for the GPIIb:IIIa complex exhibited a concentration-dependent inhibition of fibrin binding, whereas a MoAb specific for GPIb was ineffective in this regard. Similarly, a MoAb that recognizes the N-terminal region of vWF involved in GPIb binding did not influence fibrin binding. In contrast, a MoAb that binds to a C-terminal region of vWF involved in GPIIb:IIIa recognition caused a specific, concentration-dependent increase in the quantity of platelet-bound fibrin. We also found that exogenous vWF caused a concentration-dependent decrease in fibrin binding. These results support the hypothesis that vWF and fibrin, both of which are multimeric adhesive ligands, compete for occupancy of the GPIIb:IIIa complex on thrombin-stimulated platelets.
Hantgan
R R
RR
Department of Biochemistry, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27103.
Nichols
W L
WL
Ruggeri
Z M
ZM
D000911:Antibodies, Monoclonal / Q000276:immunology; D001667:Binding, Competitive; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D003592:Cytophotometry; D005337:Fibrin / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D039421:Integrin alpha2; D008562:Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011971:Receptors, Immunologic / Q000276:immunology; D013917:Thrombin / Q000494:pharmacology*; D014841:von Willebrand Factor / Q000276:immunology / Q000378:metabolism* / Q000502:physiology
D000911:Antibodies, Monoclonal; C056564:ITGA2B protein, human; D039421:Integrin alpha2; D008562:Membrane Glycoproteins; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011971:Receptors, Immunologic; C040580:glycoprotein GP III; C032193:glycoprotein receptor GPIb-IX; D014841:von Willebrand Factor; D005337:Fibrin; D013917:Thrombin